| In the Loess Plateau,large-scale artificial vegetation construction has led to the imbalance between vegetation water consumption and soil water supply,which is severely affecting the ecology of the region,at present.This is caused by the lack of understanding of the mechanism of soil water gain and loss of artificial forest land and the failure to rationally allocate vegetation in combination with limited water resources.In this paper,the deep soil water content of different vegetation types(Pinus tabulaeformis,Robinia pseudoacacia,Platycladus orientalis,apple orchard,natural forest,farmland and grassland)in Caijiachuan Watershed of Western Shanxi Province was monitored for a long time,and the rainfall infiltration and vegetation utilization of different vegetation types were studied by stable isotope technology and dye tracer experiment.The main results are as follows:(1)There was a significant difference in the amount of soil water storage in the 0-10 m soil layer under different land uses(p<0.05).Farmland had the largest value of soil water storage(1538.11mm).Robinia pseudoacacia had the lowest value(1007.65mm).Soil water storage of forest lands was significantly less than farmland and native grassland(p<0.05).Compared to grasslands,soil water of forest lands were severely feficient..(2)The soil water storage in 0-10 m soil layer of different land types was the lowest in spring(876.70mm-1416.66mm),and the highest in fall(1078.17mm-1647.77mm).Compared with the native grassland,the water deficit value of forest land was the lowest(-234.47mm)in spring and the highest(-417.6mm)in autumn.Compared with the native grassland,the forest lands was in the state of water defict in the growing season,while the agricultural land had water accumulation in the growing season.The prediction results of the model showed that the artificial vegetation might cause the water consumption of the soil layer below 10 m.(3)The water use degree of artificial vegetation on each soil layer was different.In spring,summer and fall,apple orchards mainly use water in 0-2m soil layer;Robinia pseudoacacia,Pinus tabulaeformis and Platycladus orientalis in spring mainly used the water of 0-2m soil layer;In summer,Pinus tabulaeformis and Robinia pseudoacacia used both 0-2m soil layer and 7-10 m soil layer.Platycladus orientalis used both 0-2m soil layer and 8-10 m soil layer;In fall,Pinus tabulaeformis mainly used the water of 2-10 m soil layer,Robinia pseudoacacia mainly used the water of 0-7m soil layer,and Platycladus orientalis used both 0-2m and 7-8m soil layer.(4)Rainfall and rainfall intensity have significant effects on the water absorption level of artificial vegetation after rain,.Within one week after the rainfall event with heavy rainfall(74.8mm)and high rainfall intensity(4.68mm/h),Pinus tabulaeformis,Platycladus orientalis and apple orchard mainly used water in 60-100 cm soil layer,while Robinia pseudoacacia mainly used water in 0-20 cm soil layer;Within one week after the rainfall event with heavy rainfall(97.8mm)and low intensity(2.57mm/h),Pinus tabulaeformis,Robinia pseudoacacia and Platycladus orientalis mainly used the water of 0-20 cm soil layer,and apple orchard mainly used the water of 60-100 cm soil layer;Within one week after the rainfall event with low rainfall(34.4mm)and high rainfall intensity(4.91mm/h),Pinus tabulaeformis,Robinia pseudoacacia and apple orchard mainly used the water of 0-20 cm soil layer,and Platycladus orientalis mainly used the water of 20-60 cm soil layer.(5)Under natural rainfall,there were matrix flow and preferential flow in artificial forest land,orchard and natural forest,and only matrix flow in wasteland.Artificial forest lands were more conducive to the development of preferential flow.With rainfall increased,the preferential flow ratio decreased gradually.Under the condition of artificial rainfall simulation,the infiltration depth and amount increased with the increase of rainfall,and the development degree of preferential flow and the spatial variability of infiltration water decreased with the increase of rainfall.The preferential flow was the most developed and the spatial variability of infiltration water was the largest under the condition of30 mm rainfall;Under the condition of 60 mm rainfall,the preferential flow ratio of Pinus tabulaeformis was the highest,and the spatial variability of infiltration water of Robinia pseudoacacia was the largest.This showed that the root system distribution of Pinus tabulaeformis forest and Robinia pseudoacacia forest was deeper,and the non capillary pore distribution of preferential flow is deeper and more uneven.(6)Artificial vegetation used deep soil water,resulting in the lack of deep soil water,but artificial forest lands had more non capillary pores and better development of preferential flow,which promoted the replenishment of rainfall to deep soil water and were conducive to the recovery of deep soil water.In the tending management of artificial forest land,the tending measures of deep soil moisture restoration should be taken according to local conditions,so as to alleviate the consumption of deep soil moisture by artificial vegetation,ensure the sustainable protection benefits of artificial forest land,and achieve the purpose of high-quality development and sustainable management of soil and water conservation forest in the Loess Plateau. |
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